A Multiple Input Multiple Output (MIMO) scheme refers to a scheme for improving data transmission/reception efficiency using multiple transmission antennas and multiple reception antennas, unlike a scheme using one transmission antenna and one reception antenna. That is, a transmitter or a receiver of a wireless communication system uses multiple antennas so as to increase capacity or improve performance. The MIMO scheme may be called a multiple antenna technique.
In the multiple antenna transmission technique, there are a single codeword (SCW) scheme for simultaneously transmitting N data streams using one channel encoding block and a multiple codeword (MCW) scheme for transmitting N data streams using M (here, M is always equal to or less than N) channel encoding blocks. At this time, each channel encoding block generates an independent codeword and each codeword is designed to facilitate independent error detection.
In a system for transmitting multiple codewords, a receiver needs to inform a transmitter of success/failure of detection (decoding) of each codeword. Thus, the receiver may transmit a hybrid automatic repeat request (HARQ) ACK/NACK signal of each codeword to the transmitter.